This invention relates to synthetic zeolites and their preparation and provides an improved method of preparing Zeolite NaA.
Naturally occurring or synthetic crystalline metallic alumino silicate known as zeolites have long been recognized as chemically active materials used for ion exchange or as adsorbants. The general compositional formula for a zeolite is: EQU M.sub.2/n 0.multidot.Al.sub.2 O.sub.3 .multidot.X SiO.sub.2 .multidot.yH.sub.2 O
for various types of zeolites, x and y are integers, while n is the valence of the metal, .mu.. The chemical composition, structure, physical and chemical properties of zeolites have been disclosed and discussed in numerous articles and texts. These sources include: D. W. Breck's book, Zeolite Molecular Sieves; Structure, Chemistry and Use, Wiley-Interscience; 1974. This text is hereby incorporated in this application as descriptive of the subject matter of this application and a general summation of the state of the art.
U.S. Pat. Nos. 2,882,243-4; 3,012,853 and 2,958,579 are typical of the patents teaching the preparation of zeolites. These crystalline materials are most commonly prepared by combining sources of silica, alumina and alkali, thereby forming an aqueous alumino-silicate gel. This gel is then crystallized at elevated temperatures.
The hydrothermal crystallization step required to produce zeolites has required treatment at elevated temperatures for a substantial period of time. U.S. Pat. No. 4,041,135 is typical and indicates that the crystallization step requires 1 to 6 hours. Seeding has been suggested to reduce the crystallization time. But, processes that require seeding still have crystallization steps of an hour or more. British Patent No. 1,232,429 presents some data on the reaction time but does not disclose effective methods by which the crystallization time may be reduced.
It is believed that the references indicated hereinbefore, are the most relevant to the present invention and that they provide a current picture of the state of the art of preparing zeolites.
It is an object of this invention to provide a method of preparing Zeolite NaA in which the time required for crystallization is a small fraction of the time required in the prior art practice.